intel/compiler: Create and use struct for CS thread payload

intel/compiler: Create and use struct for CS thread payload

Move subgroup_id, that's only used by CS for verx10 < 125, as part of
the payload too -- even though is not, strictly speaking.

Note the thread execution of Task/Mesh is similar enough, so we make
their common struct inherit from cs_thread_payload.

Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18176>